Question

For the octahedral complexes of Fe³⁺ in SCN^- (thiocyanato-S) and in CN^- ligand environments, the difference between the spin-only magnetic moments in Bohr magnetons (When approximated to the nearest integer) is 

[Atomic number of Fe = 26]

Answer 1

In both the cases the electronic configuration of Fe³⁺ will be

1s² , 2s² , 2p⁶ , 3s² , 3p⁶ , 3d⁵

Since SCN is a weak field ligand and CN is a strong field ligand, the pairing will occur only in case of [Fe(CN₆)^3-

Difference in spin only magnetic moment = 5.91 – 1.73 = 4.18 ≈ 4